U.S. Pat. No. 6,361,173, describes an image projection system in which a matte signal selectively inhibits the projected image within the silhouette area of a presenter when in front of the projection screen.
In the U.S. patent application Ser. No. 10/370,356, a projected infrared pattern on the presenter is displaced from the surrounding pattern on the unobscured screen area when viewed by an infrared camera displaced a few inches from an infrared projector. Except in the area of the presenter, the two patterns subtract to zero.
The complexity of projecting an infrared non-repetitive pattern and obtaining a camera image of such a pattern at high resolution has lead to the development of a less complex matte generation method described below.
A white projection screen containing a small number of infrared retro reflective elements, uniformly distributed over the screen""s surface, is illuminated by an infrared source and observed by a coaxially located infrared camera. A matte signal is generated utilizing a high signal level from the infrared camera in all unobscured areas on the screen, and a very low signal level in screen areas obscured by a presenter between a projector and the projection screen.